Abrasive type cutting element and the manufacture thereof



Patented Feb. 28, 1950 ABRASIVE TYPE CUTTING ELEMENT AND TEE MANUFACTURE THEREOF Geo'xge Davies, Welwyn, England, asslgnox to Arthur Percy Warten, Esst 'lwlckenham, England Appllcation April "l, 1947, Serlal N0. 739,841. In Grea.t Britain September 10, 1945 Sectlon l, Publlc Law 690, August 8; 1946 Patent expires September 10, 1965 11 Clulms. 1

This invention relates to abrasive tools provlded with metal cutting faces er edges and the manufacture thereof.

Exlsting abraslve tools fo1med irom' carborundum end similar mineral substances are comparatively fragile which limits the dimensions und shape in which they can safely be frmed and used. Further many of them show an inclination to clog end require frequent trimming which consumes them; while further they have poor thermal conductivity so thal; they do n'ot carry away readily the frictional heat formed -by their use. Again since their use entails the continual disintegration of their working surfaces they lose shape and size and create dust which has to be extracted or carried away by liquid and has subsequently to be disposed of. Thls applies to abrasive tools used both in indu stry and in such professions as in dentlstry.

The object of the present invention is to provide improved metal-working tools end. methods of manufacturing them which will reduce or overcome the difficulties encountered in the use cf abrasive tools as heretofore made.

T0 'bhis end according to the present invention my lmproved tool has a metallic Cutting surface which is produced by forming pits or depressions therein end then coating the surface electrolytically with chromium or Iike hard m'etal in the shape of minute projections or nodules, which when broken otf leave a multitude of sharp edges.

Preferably the chromium is applied in a known manner at such current density es to build up on the raised parts of the surface adjacent -to the pits or depressions, forming a series of globules or nodules which are then broken 01T so as each to 1eave exposed the broken and highly abrasive surface of the nexus by which each globule was joined to the base metal.

The pits or depressions may.be produced in any one of a number of ways, for example by mechanical means, by chem'lcal means or electrochemical means, or a combination of such means.

In most cases the surface after or before pitting and before plating will be hardened but in other cases the metal surface 1nay initially be Sufficiently hard not to require hardening before plating. Further, where hardening is used, it Will in many cases be desirable, particularly where the part to which the abrasive surface is to be applied is of small cross-section, as in the Gase of small files or wire which is to be rendered abrasive, to harden the base metal by rolling, drawing or swaging instead of by heattreatmnt since it has been 1'ound that metals so hardened by working are less llable to hydrogen embrittlem'ent when chromium plated than meta.ls hardened by heat-treatment. It will be understood that such work hardening by dra.wing, swaging or rolling would normally ha.ve to be done bef ore forming the pits or depressions end that usually in such instances therefore these would be forme'cl by chemical or electrochemical means rather than by mechanical means.

- The invention may be applied to a. large variety of abrasive tools und may be applied to surfaces of a large variety of forms; One application of the invention is. however, shown purely by way of exam'ple in the accompanying drawings, in which:

Figure 1 is a front elevation cf a disc havin an abrasive rim according to the invention;

Figure 2 is a side elevation of the disc shown in Figure 1;

Figures 3, 4, 5 and 6 show in cross-section and on a, greatly enlarged scale sections of the rim of the disc shown in Figures 1 and 2 at various stages in the production thereon of an abrasive surface according to the invention, the section being taken on the line III-III of Figure 2;

Figure.7 is a still further enlarged view of a small section of the surface of the abrasive wheel at the stageshown in Figure 5 and Figure 8 is a, similar view to Figure 7 but taken a.t the stage shown in Figure 6.

In the form of the inventio n illustrated, the disc is mounted upon a rotational shaft A and has an abrasive rim A according to the inventi0n. This abrasive rim is produced in the following manner: First, the rim is pitted as indicated in Figure 3, either by mechanical means or by chemica1 o1 electro-chemica-l methods, for example, by first starting corrosion by dipping in streng hydrochloric acid and then enlarging the pits by causing some of the pits to merge into others by hanging the disc in an atmosphere charged with nitric acid fumes. This results in the production of the pits (which, though irregular, are of generally wund shape) in the surface of the metal end, as will be appreciated, is really a process of artificial and controlled rusting. The process is arrested when the pits are cf a size 'corresponding to the grit required in the abrasive surface.

Sometimes a grain is useful in the abrasive surface and this may be secured by alternating exposure of the surface to be pitted to the nitric acid atmosphere with exposure' to liquid hydrochloric acid or by varying the duration cf action of the two treatments, it being found that the acid fumes tend to produce circular pits, while the liquid acid tendl to produce linear pits or to canvert round pits into linear or vermiiorm pits.

The pits should, as shown, be comparatively deep with oomparatively sharp edges. Further, the suriace 120 be pltted may be hardened. i!or example. lrv helt treatment beton or alter pitting. Where the pits are iormed mechanically, they may be produced in known manner by vibratory steel needle points or by a rotating chain man. the links of which have rasplike prajections. and it will be understood that in this dase it the pitted suriace is to be hardened;such hardening would conveniently be carried out alter pittinz.

In any case, the pitted suriace as shown at A in Figure 3, is cleaned, ior example, in hydrachloric acid rinsecl and then placed in an electrolytic platlng bath o! hard chromium' solution; through which a heavy current is passed in the normal manner. Thls results in a thick deposit of chromium being deposlted round each 015 the pits, the deposit startlng somewhat as indicated at A in Figure 4 and then building up into nodules as lndicated at A in Figure 5, euch connected to the metal o! the rim o1 the disc A by a nexus A,

as shown most clearly in Figure 7. After plating to this stage, which may take a matter of a few minutes, the disc A is removed from the plating bath, rlnsed, and the globules A are broken 011 as shown in Figures 6 and 8. Thls leaves exposed the broken suriace A" of each nexus which canstitutes in efi'ect a sharp tooth o1 grain" 01 abrasive type cutting metal.

It will be appreciated that by varying the size, form and spacing oi the pits lt is readlly possible to produce the requlred grlt in the flnished disc. It will also be understood that when the disc ls exposed to chemical action during production 01 the abrasive surface thereon, surfaces which are not to be rendered abraslve may be shlelded from chemical action' elther by approprlate solid shields or by wax or other suitable materlal applied to them.

Further, although the disc shown by way oi' example in the drawings is of appreciable width. lt will be underst0od that discs with abraslve rims according to the inventlon may be made of considerably thlnner sect-lon than carborundum or slm'ilar mineral abrasive discs without risk of fracture, while, owing to the iact that the rim A can readily be made sllghtly wider than the remainder of the disc blndlng in the work being treated by the disc can be reduced 01' eliminated.

When the abrasive surface of a disc as shown in the drawings requlres renewal, this suriace can readily be re-coated with chromium nodules and the nodules broken oiI at small cost and in a very short time, so as 1:0 provlde a new abraslve surface.

The breaking-ofl of the nodules may be carrled out for example by means of a stltf wire brush or by scraplng with a hard metal edge, whlle moreover the nodules so broken ofl may be used. if desired, for pitting softer materials, as by presslng or rolling them lnto the suriface thereof and then scouring them ofl.

It will be understood that the normal precautions necessary when chromiun'x-plating must be taken. such, for example, as carrylng out the plating immediately alter cleaning and rinsing a surface to be plated, in order to ensure 800d adherence of the chromium coat to the base metal.

In an alternative example of the invention, steel rod, strip or wire, which is to be rendered abrasive may have hardness imparted to lt by rollin'g.

4 drawing or swifli8. the material thus work hardened then having pits i'ormed in lt, tor example. by a chemical or electro.-chemical process. an mentioried above, i'ollowed by plating an described. lt will be readily underatood that the iorm 01 the material or surtaces to whlch the inwiention is applieci may vary within very wide limits and that abrasive tools according to the invention may thus similarly vary widely in f0rm' according to their intended use. I"urther materials carrying abrasive surfaces according to the invention can be in forma in which sati.sfactory abrasive surfaces could not previously be provided. For example. abrasive wires may be made according to the invention by treating drawn steel wire by a chemical pitting process tollowed by chromium coating as described and brushes may be made i'rom auch wires and will then be capable oi, abrading metal objects ot auch shapes that a solid abraslve tool cannot nach all the parts 01 the surface to be abraded or even for such purposes as frosting" a pane oi glass.

It is thus to be understood that both the method of manufacturlng the abrasive surfaces according to the invention and articles according to the lnventlon having auch abraslile surfaces may vary very widely without departing i'rom this Invention.

What I claim as my invention and desire to secure by Letters Patent is:

1. A method 01 forming an abraslve type cutting element according to which a metal surface to be renderecl efl.ective for ci1ttlng has pits or depresslons formed therein, a hard metal suitable for electro-plating 011 said suriace is then applied electrolytically to the pitted suri'ace to build up a serles of nodules around the pits and the nodules are then broken ofl, leaving exposed the broken and highly abrasive surface o! the nexus by which each nodule was jolned to the base metal.

2. A method of forming a cutting element accordlng to claim 1 whereln the metal surface to be rendered eilfective for cutting is coated electrolytlcally with chromlum.

3. A method of formlng a cuttlng element as claimed in clalm 1, in whlch after pltting and before plating the surface is hardened.

4. A method cf formlng a cutting element as claim'ed in clalm 1, in which the base metal on which the hard metal ls to be deposlted is work hardened by working prior to pitting and plating.

5. A method of forming an abrasive type cutting element accordlng to which a metal surface to be rendered eflfective for cutting has pits or depresslons formed thereln by chemlcal attack, a hard metal suitable i'or electro-plating on sald surface is applied to the pltted surface electrolytically to build up a series of nodules around the pits, and the nodules a.re then broken all? so as to leave exposed the broken and highly abrasive surface of the nexus by which each nodule was joined to the base metal.

6. A method oi formlng a cutting element as claimed in claim 3, in which the base metal an whlch the hard metal is to be deposited is work hardened by worklng prior to pitting and plating.

7. A method of formlng a cutting element as claimed in claim 3, in whlch the base metal ls ferrous and the pits are formed by first treating the surface with streng hydrochlorlc acid rinsing the surface and then subjtecting the surface to n itric acld fumes.

8. A method of formlng a cutting element as claimed in claim 3, in which the base metal is ferrous and the pits are formed by subjecting the 5 A surface alternately two or more times to trautment by hydrochloric acld followed by treatment by nitric acid fumes.

9. A method oi forming an abraslve type enttlng element according to whlch the surface of a ferrous d1sc to be rendered abrasive has pits or depressions formed there1n and 1s then coated electrolytically with chromium to forni nodules on said surface, following which said nodules are braten 011 close to sa1d surface to provide a multitude of highly abrasive broken nexus thereon.

10. A cufiting tool including, a. metallic body providing a surface, an irregularly scattered but closely spaced plurality of fine projections extending outwardly from the surface generally a.t right angles thereto, each projection terminating in s. chromium top whose end surface comprises a plurality cf irregular sharp jagged projections of uneven outward extent, the terminus of said Jagged projections defining, in the main, a. surfa.ce conforming in outline to said flrst mentioned surface to provide a cutting area.

11. A cutting tool including a metallic body providing a surface comprising an irregularly scattered but closely spaced plurality cf fine pro- :lect1ons extending outwardly therefrom, each projection terminating in a, top of hard metal auch as chromium adherent to sa1d body whose end surtace oomprises a plurality o1 irregular sha.rp jagged projections 01 uneven outward extent, the terminus of sald jagged projections deflning, in the main. a surface conforming in outline to said flrst mentioned surface to provide a cutting area.

GEORGE DAVIES.

REFERENCES CITED The following references are 015 record in the flle of this patent:

UNI'IED STATES PATENTS 2314,604 Van der Horst Mail. 23, 1943 

